Microwave and monolithic microwave modules have been formed in which the circuits themselves are mounted into a passive electrically conductive housing or carrier and have active electronic elements such as filters, mixers, switches, amplifiers, and the like epoxied or soldered to the interior of the housing, with a top lid hermetically sealing the housing. The devices are made of plates or sheets of conductive material such as metals which have to be manufactured by ion milling to exceedingly high tolerances.
The reason for the high tolerances is that one seeks to minimize losses through the monolithic microwave integrated circuit, with the losses resulting from dimensional inaccuracies which can cause detuning of the circuit because it varies the propagation structure and because roughened surfaces result in mismatches and/or circuit losses.
In order to provide a prototype for a final microwave assembly, the prototyping process in the past has required multiple different steps starting with the circuit designer. The circuit designer will design a module utilizing some sort of drawing. The drawing is then transferred to a machine shop which requires that the drawing be put in a CAD CAM format so that a solid blank of material can be hogged out and then microfinished to the required dimensions by etching, grinding or milling. This requires a numerical control (NC) tape, with the milled product then being transferred to a plating shop at which point, for instance, gold plating is sputtered onto an appropriately patterned metal housing.
Because of the multiple steps involved, oftentimes, the resulting prototype doesn't fit or is improperly dimensioned so that one then has to go back through the above process in order to provide a prototype model that will operate properly.
It will be appreciated that in monolithic microwave integrated circuits, a number of active elements are soldered or conductive-epoxied to the plating in order to provide for the appropriate functioning of the circuit.
While soldering per se is not a problem when the module housing is made of solid metal, it does become a problem if other housing materials are utilized.
The above process may take a matter of several weeks in order to provide a prototype which is testable and for this reason there is a need for a rapid prototyping process which reduces costs and turnaround time to hours or days.